The effect of photocatalysis has been known for a long time and is utilized in particular for oxidizing and/or degrading organic compounds (e.g. soiling) on substrates under sunlight or artificial light. The same oxidation reaction can be used in the chemical industry and in the water processing field, for example, for selectively oxidizing or degrading chemical compounds and microbes.
Photocatalytically active coatings must have adequate mechanical and chemical stability. This should not be at the expense of the activity of the coating; the coating must exhibit an adequate amount of activity even under modest solar radiation, e.g. during the winter.
Photocatalytic coatings are already known. In the case of plastic substrates or painted substrates (e.g. painted metal sheets), however, a protective layer must be applied in order to prevent oxidation of the substrate, said layer being then covered by the actual photocatalytically active layer. This double coating is disadvantageous in terms of production costs and service life of the systems.